Technical Abstract:
Agricultural biomass represents an abundant renewable resource that can be used for the production of fuel ethanol. However, its use is limited in part by the expense of converting this complex substrate, that is composed of cellulose and hemicellulose (glucans, xylans, mannans, and arabinans), into fermentable sugars. Additionally, few organisms are capable of fermenting all the hydrolyzed components to ethanol. Several filamentous fungi secrete a wide array of cellulases and xylanases and are able to convert most types of agricultural biomass directly to ethanol. Unfortunately, reported fermentation rates and yields are quite low. We previously demonstrated that it was possible to improve ethanol fermentation in the fungus Aspergillus nidulans by heterologous expression of the Zymomonas mobilis pyruvate decarboxylase gene. While A. nidulans was a useful tool for this study, final ethanol concentrations were still low and mycotoxin production limits its potential use for large scale fermentations. The Aspergilli, particularly those used in food applications, are desirable because of their safety and efficient utilization of diverse substrates. We have screened over 20 Aspergilli for their ability to ferment simple sugars (glucose, xylose, and arabinose) as well as complex substrates (cellulose, oatspelt xylan, corn cob, and corn germ pressing). Combined fermentations utilizing both Aspergilli and yeast were also examined. Results will be presented that demonstrate that at least one strain of A. oryzae may be a suitable organism for ethanol studies and should be examined further.